1. Field of the Invention
The present invention relates to a fluid-filled vibration damping device to be used for an automotive engine mount and the like, for example.
2. Description of the Related Art
Conventionally, there has been known a vibration damping device as a kind of vibration damping coupling body or a vibration damping supporting body interposed between the members constituting a vibration transmission system to connect the members to each other in a vibration damping manner. In addition, for the purpose of improving the vibration damping performance, a fluid-filled vibration damping device using the vibration damping effect based on the flow action of a non-compressible fluid sealed therein is proposed. The fluid-filled vibration damping device has a structure where a first mounting member and a second mounting member are elastically connected by a main rubber elastic body, and a pressure-receiving chamber whose wall is partially constituted by the main rubber elastic body and an equilibrium chamber whose wall is partially constituted by a flexible film are formed, each containing a non-compressible fluid sealed therein, while an orifice passage is formed to connect the pressure-receiving chamber and the equilibrium chamber to each other.
Meanwhile, in case of a fluid-filled vibration damping device, cavitation noise generated at a shockingly large load input can become a problem. The cavitation noise is generated and sensed as an abnormal sound when a rapid local pressure drop occurs in the pressure-receiving chamber due to a large load input to cause local boiling of the non-compressible fluid or air bubbles due to the gas-liquid phase separation and the like of dissolved gas in the pressure-receiving chamber, and then, the air bubbles burst up by cancellation of the pressure drop so that the shock wave produced by the bubble burst is transmitted to the vehicular body to be felt as noise.
In order to prevent generation of air bubbles by means of cancelling the negative pressure in the pressure-receiving chamber as soon as possible, a fluid-filled vibration damping device formed with a short-circuit passage that communicates the pressure-receiving chamber and the equilibrium chamber to each other and provided with a valve that switches on and off the communication via the short-circuit passage has been proposed as disclosed in Japanese Unexamined Patent Publication No. JP-A-2003-148548. According to JP-A-2003-148548, once internal pressure of the pressure-receiving chamber drops down significantly at a shockingly large load input, the short-circuit passage shut off by the valve is switched to a communicating state so that the pressure-receiving chamber and the equilibrium chamber are communicated to each other by a short-circuit passage with small flow resistance. This allows the fluid to flow from the equilibrium chamber to the pressure-receiving chamber via the short-circuit passage to reduce the negative pressure in the pressure-receiving chamber, thus preventing generation of air bubbles caused by cavitation and avoiding the cavitation noise.
However, since the structure of JP-A-2003-148548 requires a valve that opens and closes at a given pressure, there was a problem of having difficulties in avoiding an increase in the number of components and more complex structure.